22 METHODS OF ANALYSIS. 



(d) CARBON, SAND, AND SILICA. 



Transfer the residue from the carbon dioxid determination to a beaker or 

 evaporating dish ; evaporate to dryness and thoroughly dry and pulverize to 

 render silica insoluble. Moisten the dry residue with from 5 to 10 cc of hydro- 

 chloric acid, take up with about 50 cc of water, allow to stand on the water 

 bath for a few minutes, filter through a parchment-paper filter (S. and S. 

 "hardened" filters), and thoroughly wash. Make the solution and washings 

 up to 250 cc or other convenient volume and preserve for analysis. Designate 

 as Solution A. 



(1) Wash the residue from the filter (which may be used again) into a 

 platinum dish and boil about 5 minutes with approximately 20 cc of a satu- 

 rated solution of pure sodium carbonate, add a few drops of pure sodium 

 hydroxid solution, allow the solids to settle, and decant the liquor through a 

 tared gooch. Boil the residue in the dish with sodium carbonate solution and 

 decant as before. Repeat the process a third time, after which bring the 

 residue upon the filter and thoroughly wash, first with hot water, then with a 

 little dilute hydrochloric acid, and finally with hot water until free from 

 chlorids. Dry the gooch and contents to constant weight at 110 C., thus 

 determining the combined weight of carbon and sand. After incineration the 

 loss in weight gives the carbon. It is advisable to examine the residue under 

 the microscope to ascertain if it is really sand. The alkaline filtrate and wash- 

 ings are united, acidified with hydrochloric acid, evaporated to dryness, and the 

 silica separated and determined in the usual way. 



(2) Instead of determining directly the silica dissolved by the sodium car- 

 bonate solution, as described above, another portion of the ash may be treated 

 as in 2 (c) and (d), and the residue of silica, sand, and carbon filtered on an 

 ordinary filter, washed, burned, and weighed, giving the combined weight of 

 silica and sand, from which the weight of sand found in 2 (d) is to be deducted 

 to obtain the silica. It is inadmissible to separate the soluble silica from the 

 residue after ignition. 



Subtract carbon, carbon dioxid, and calcium oxid, added in the form of cal- 

 cium acetate, from the ash, and calculate results as carbon-free ash. 



3. Manganese, Calcium, and Magnesium. Official. 



To an aliquot of Solution A, corresponding to 0.5 to 2 grams of ash, add a 

 quantity of pure ferric chlorid solution, more than equivalent to the phosphoric 

 acid which may be present, neutralize with ammonium hydroxid, dissolve the 

 precipitate in a very slight excess of hydrochloric acid, add 1 or 2 grams of 

 sodium acetate, and boil one or two minutes, filter at once, and wash with boil- 

 ing water. Dissolve the precipitate in hydrochloric acid and reprecipitate as 

 above. Evaporate the filtrate and washings to about 50 cc, and determine man- 

 ganese, calcium, and magnesium as in the analysis of soils ((c), (d), and (e), 

 p. 15). The quantity of calcium found must be corrected for the calcium added. 



4. Phosphoric Acid. Official. 



(1) In an aliquot of the hydrochloric-acid solution, corresponding to from 

 0.2 to 1 gram of ash, determine phosphoric acid by either of the methods for 

 total phosphoric acid given under fertilizers ((a) (2) or (6) (2), pp. 2 and 4). 



(2) The determination can also be made in the plant substance as in (a) 

 (2), page 2, for determining total phosphoric acid in fertilizers, using sufficient 

 material to give from 0.2 to 1 gram of ash in the aliquot of the solution used. 



